For the past decade or so, I’ve been of the mind that you can always judge a restaurant by the quality of its bread and butter. It might seem a bit neurotic, but if the butter doesn’t come to the table at a spreadable temperature, or if the chef decides that it’s smarter to bake his own leather-crusted bread than to order out, it can ruin a meal before it’s even started.

But these days, there’s a new unctuous bread-spread in town: bone marrow. Thanks to chefs such as Anthony Bourdain, Fergus Henderson, and their offal-minded ilk, it’s not uncommon to see sawed-off sections of beef shin emerging from bistro and chophouse kitchens around the gentrified world. And if restaurants can be ranked by their marrow, KO Prime sits high on its throne.

At most places, it’s a minimalist affair: scoop a bit of gelatinous marrow out of the bone, spread it thick on a crisp piece of toast, eat, smile, and sigh contentedly. KO Prime’s got all these bases covered and then some. Rather than the usual lengthwise split, their bones are left whole, which is a good thing — it traps the copious amount of rendering fat released as it roasts, essentially cooking the marrow in its own juices. The paper-thin toast it’s served with performs its function as delivery device and crunchy, unobtrusive foil to the tongue-coating marrow, while coarse sel gris and Dijon mustard cut through the richness with sharp heat. A few vinegary pickled shallots and parsley sprigs cleanse your palate for the next bite. Just as you finish the third of the three-inch long bones, the icing on the cake reveals itself: a sticky mound of oxtail marmalade under the bones that absorbed every fatty drop of juice dripped onto it. The result is three bites so insanely rich and beefy you’ll wonder if the Wagyu steak you ordered to follow it might be a letdown (it’s not).

Available for $13 at KO Prime, 90 Tremont Street, in Boston. Call 617.772.0202.